A self-aligning journal bearing having tiling pads has been used as a journal bearing of a large size rotating machine.
A journal bearing having tilting pads devised by the applicant of this application is disclosed in patent literature 1 (Japanese Laid-Open Patent Application No. 5-332355). As disclosed in the patent literature 1, each of the tilting pads is supported by means of a spherical pivot and an adjusting liner received in a recess defined in the back side face of the tilting pad and in a recess defined in the inner side face of the bearing housing such that the pad is swingable about an axis parallel with the rotation shaft (circumferentially swingable) and about a direction perpendicular to the axial direction of the rotation shaft (axially swingable).
As the pads are swingable circumferentially and axially in accordance with the movement of the journal, a journal bearing of tilting pad type has self-aligning function.
Therefore, it can support a journal stably and is preferably adopted for high speed rotating machines.
The spherical pivot is received in both the recess in the tilting pad and the recess in the bearing housing so that it serves as a stopper of the tilting pad, i.e. the tilting pad is prevented from being dragged circumferentially by the rotation of the journal.
There are two types of tilting pad journal bearing, i.e., oil flooded lubrication type and direct lubrication type. In the oil flooded lubrication type, both axial end sides of the tilting pad are sealed so that spaces between a tilting pad and the adjacent tilting pad are flooded with lubrication oil. With this type, mechanical efficiency decreases due to friction loss of the side seals and agitation loss of oil in the spaces between the tilting pads.
Occurrence of decrease of mechanical efficiency will be explained referring to FIG. 8 quoted from the patent literature 1. FIG. 8 is a graph showing a relation between mechanical loss and rotation speed of journal in a journal bearing of oil flooded type. In the graph, the total mechanical loss increases nearly proportional to the square of the rotation speed. It consists of frictional loss X between the journal surface and bearing surfaces of the lower pads on which bearing load exerts, frictional loss Y between the outer circumference of the journal and bearing surfaces of the upper pads on which bearing load does not exerts, and mechanical loss Z which is the sum of the friction loss due to the side seals and agitation loss of oil in the spaces between the pads due to agitation by the rotation of the journal.
Direct lubrication type of tilting pad radial bearing was proposed to eliminate the mechanical loss Z. In the direct lubrication type, oil supply nozzles are provided at the upstream side of each tilting pad upstream in relation to journal rotation direction and lubrication oil is supplied to the bearing surface of each tilting pad, and side seals are eliminated. Direct lubrication type is now widely adopted, as mechanical loss Z can be eliminated. The tilting pad journal bearing of the patent literature 1 is of direct lubrication type.
Another type of direct lubrication type tilting pad radial bearing is proposed in patent literature 2 (Japanese Laid-Open Patent Application No. 2000-274432). In a tilting pad journal bearing of direct lubrication type, there is a problem of so-called carryover of lubrication oil as recited in paragraph [0009] of the patent literature 2. This is a phenomenon that the lubrication oil lubricated the bearing surface of an upstream tilting pad is carried on the rotating journal to be introduced to the bearing surface of the adjacent downstream tilting pad.
Lubrication oil rises in temperature in the interstice defined by the circumferential surface of the journal and bearing surfaces of the tilting pad (hereunder referred to as bearing clearance of the tilting pad) due to shearing force in the lubrication oil in the interstice caused by the rotation of the journal. Lubrication oil increased in temperature in the bearing clearance of the upstream tilting pad is carried over to the bearing clearance of the adjacent downstream tilting pad, so the lubrication oil is further increased in temperature in the bearing clearance of the downstream tilting pad, which may cause overheat of the bearing surface of the tilting pad and occurrence of bearing seizure.
Means of preventing carryover of lubrication oil in a direct lubricating type tilting pad journal bearing are proposed in the patent literature 2.
In patent literature 3(Japanese Laid-Open Patent Application No. 2006-112499) is proposed another means of preventing excessive temperature rise of lubrication oil in a direct lubricating type tilting pad journal bearing. With this means, an oil supply nozzle is provided to the bearing housing at each of the upstream side end and downstream side end of a tilting pad in relation to the rotation direction of the journal, and a cooling path is formed in the pad circumferentially parallel with the bearing surface of the pad. A part of oil injected from the oil supply nozzle located at the downstream side end is directed to be introduced into the cooling path, thereby cooling the bearing surface of the tilting pad from under the bearing surface thereof to suppress temperature rise of the bearing surface.
As recited in paragraph [0004] of the patent literature 2, a bearing clearance of a tilting pad (clearance between the journal surface and bearing surface of the tilting pad) is filled with lubrication oil, the pad is supported by the stationary bearing housing, and the journal rotates at high speed in the oil filled in the clearance. Therefore, very large speed difference is developed in the oil between the bearing surface of the pad and journal surface. A wedge-form oil film is formed between the bearing surface of the pad and journal surface due to the speed difference, and oil pressure is generated in the oil film to support load exerted from the journal onto the bearing surface of the pad.
FIG. 9, which is a quotation of FIG. 33 of the patent literature 2, shows pressure distribution in the lubrication oil film between the journal surface and bearing surface. In the drawing, a plurality of tilting pads 101a˜d are disposed around the journal 100 to support the journal 100. Radial clearances 102 between the journal 100 and the tilting pads 101a˜d are filled with lubrication oil. Integration of oil film pressures Fp exerting to the bearing faces of the pads 102 coincides with the bearing load W.
High oil film pressure is generated by the effect of wedge shape of the oil film narrowing the radial clearances 102 downstream of rotation direction of the journal due to tilting the each tilting pads 101a˜d. 
A direct lubrication type tilting pad journal bearing is superior to an oil flooded type tilting pad journal bearing in a point that mechanical loss is smaller in the former than in the latter, as mentioned above.
However, construction becomes complicated in a direct lubrication type tilting pad journal bearing because of providing oil supply nozzles and/or adopting means to suppress carryover of lubrication oil, resulting in increased manufacturing cost.
In a tilting pad journal bearing, not only the direct lubrication type tilting pad journal bearing, tilting pads are supported swingable circumferentially and axially in relation to the journal by spherical pivots provided in the inner face of the bearing housing and the swingable supporting structure makes assembling and disassembling of the journal bearing too much like hard work. With the present structure of the journal bearing, tilting pads can be detached from inside the bearing housing only after detaching the journal bearing because the spherical pivots protrude from the bearing housing into recesses in the back face of the tilting pads.
As self weight of the rotation shaft exerts on the bearing surface of a lower tilting pad disposed on the inner face of the lower bearing housing, high pressure oil film is formed relatively easily on the bearing surface of the lower pad as the journal rotates. However, self weight of the rotating shaft does not exert on the bearing surface of an upper tilting pad disposed on the inner face of the upper bearing housing, so high pressure oil film can not be formed easily.
Further, when adjusting radial clearance between the bearing surface of a tilting pad and rotating surface of the journal so that a radial clearance narrowing toward downstream of rotation direction of the journal is formed between the bearing surface of a lower tilting pad and rotating surface of the journal in order to allow high pressure oil film on the bearing surface thereof as the journal rotates, the adjusting is not easy in the case of journal bearing of large rotating machines, for self weight of the tilting pad increases.    Patent literature 1: Japanese laid-open Patent Application No. 5-332355.    Patent literature 2: Japanese laid-open Patent Application No. 2000-274432.    Patent literature 3: Japanese laid-open Patent Application No. 2006-112499.